Rising carbon dioxide levels reduce nutrients in staple crops

MARK COLVIN: Scientists are again warning that the dangers of climate change will be more wide-reaching than rising sea-levels and wilder weather.

New research suggests the nutrition levels of staple foods will fall as the amount of carbon dioxide in the atmosphere rises.

They fear it'll erode decades of progress battling global malnutrition unless they can find a solution.

Simon Frazer reports.

SIMON FRAZER: Carbon dioxide is a major factor driving global warming, but it's also the essential ingredient that allows plants to harness the energy of the sun.

Even so, new research published in the journal Nature suggests vegetation can have too much of a good thing.

The study's lead author is Samuel Myers from Harvard University's Center for the Environment in the United States.

SAMUEL MYERS: Rising concentrations of carbon dioxide in the atmosphere are threatening global human nutrition by reducing the amounts of very important nutrients for human health in important food crops like rice, wheat and soy beans, and in particular, we found significant reductions in zinc, iron and protein.

SIMON FRAZER: Rice and wheat are heavy lifters in the task of feeding more than 7 billion humans around the world.

Dr Myers says nutritional changes in those grains in the future risk making a significant problem now worse.

SAMUEL MYERS: There are roughly 2 billion people around the world who suffer from these deficiencies, and ultimately zinc deficiency affects our immune functions. So, much of the burden of disease is calculated through early child mortality from infectious diseases like malaria and diarrhoea, pneumonia, measles. And for iron deficiency, we see anaemia, but we also see sharp increases in maternal mortality, loss of IQ, reduced work productivity.

SIMON FRAZER: The study's results are based on trials of six common crops at sites in the US, Japan and Australia.

Glenn Fitzgerald is a co-author who runs a carbon dioxide testing program at Horsham for Victoria's Department of Environment and Primary Industries.

His team grew wheat and field peas in a specially adapted open field.

GLENN FITZGERALD: Currently, future levels are around 400 points per million, and we're elevating them to 550, which is predicted for 2050.

So, that's done through a series of horizontal pipes that are joined and they get raised up on posts as the crop goes so that they sit just above the top of the crop, and injects CO2. It's all computer controlled in terms for wind speed, direction and central concentration of CO2.

GLENN FITZGERALD: It does depend on environment, rainfall, temperature et cetera. But here at Horsham, we're seeing, on average, an increase of about 20-25 per cent increase in yield, but you also get then this 5-10 per cent decrease in protein and zinc and iron concentrations.

SIMON FRAZER: Those in the developing world are more susceptible to falling nutrition levels in staple plants because they're less likely to have regular access to other foods to fill the gap.

Dr Fitzgerald says they're now looking at potential solutions, including breeding new varieties.

GLENN FITZGERALD: Then perhaps we can counteract some of these negative impacts that are occurring due to CO2.

Another way of doing that potentially is through nitrogen management. Can we add nitrogen fertilisers at the right time or in the right way, meaning slow-release fertilisers or foliate fertilisers et cetera, in order to counteract that negative impact of carbon dioxide?

SIMON FRAZER: But with the long lead time needed to develop new varieties, alternative staples may also need to be considered.

Dr Fitzgerald says the study suggests crops such as corn may be less affected.

GLENN FITZGERALD: These crops have evolved to be more efficient already in their uptake of carbon dioxide, so adding more carbon dioxide doesn't necessarily stimulate them in terms of growth.

However, we do see some changes in, again reduction in protein and micronutrients, but not as severe as in other crops.